Time-lag measurement of void discharges for the clarification of the factor for partial discharge pattern

Time-lag of void discharges was measured in order to establish the physical model for the formation of partial discharge pattern under AC voltages. The measurement with step voltages, using CIGRE Method II electrode system, showed that the statistical distribution of the discharge time-lag depends on the applied voltage, the time lag being shorter with increasing the voltage. In most cases, the statistical scatter of the time lag under the same step voltage fitted with a straight line on the Laue Plot, indicating that the time-lag follows the exponential distribution. The characteristic time-lag decreased with the magnitude of step voltage, and followed the inverse power low. The decline of the “time-lag vs. voltage” plot was correlated to the partial discharge pattern under the AC voltage. Moreover, the time-lag distribution with different kinds of specimens were compared together, in order to explain the difference in partial discharge pattern under AC voltage. It was concluded that the discharge time-lag plays an important roll in generating the partial discharge pattern, and that some features of the pattern can qualitatively be explained by the voltage dependence of the discharge time-lag